https://sourceware.org/ml/gdb-patches/2014-09/msg00156.html
Message-Id: <1409947102-32166-1-git-send-email-emachado@linux.vnet.ibm.com>

commit 2e4bb98a0e52acbb2da4ae441b89a568af26adf8
Author: Edjunior Barbosa Machado <emachado@linux.vnet.ibm.com>
Date:   Mon Sep 8 13:37:23 2014 -0300

    Fix ppc_collect/supply_ptrace_register() routines
    
    This patch fixes the routines to collect and supply ptrace registers on ppc64le
    gdbserver. Originally written for big endian arch, they were causing several
    issues on little endian. With this fix, the number of unexpected failures in
    the testsuite dropped from 263 to 72 on ppc64le.
    
    gdb/gdbserver/ChangeLog
    
    	* linux-ppc-low.c (ppc_collect_ptrace_register): Adjust routine to take
    	endianness into account.
    	(ppc_supply_ptrace_register): Likewise.

Index: gdb-7.6.1/gdb/gdbserver/linux-ppc-low.c
===================================================================
--- gdb-7.6.1.orig/gdb/gdbserver/linux-ppc-low.c
+++ gdb-7.6.1/gdb/gdbserver/linux-ppc-low.c
@@ -170,25 +170,52 @@ ppc_cannot_fetch_register (int regno)
 static void
 ppc_collect_ptrace_register (struct regcache *regcache, int regno, char *buf)
 {
-  int size = register_size (regno);
-
   memset (buf, 0, sizeof (long));
 
-  if (size < sizeof (long))
-    collect_register (regcache, regno, buf + sizeof (long) - size);
+  if (__BYTE_ORDER == __LITTLE_ENDIAN)
+    {
+      /* Little-endian values always sit at the left end of the buffer.  */
+      collect_register (regcache, regno, buf);
+    }
+  else if (__BYTE_ORDER == __BIG_ENDIAN)
+    {
+      /* Big-endian values sit at the right end of the buffer.  In case of
+         registers whose sizes are smaller than sizeof (long), we must use a
+         padding to access them correctly.  */
+      int size = register_size (regno);
+
+      if (size < sizeof (long))
+	collect_register (regcache, regno, buf + sizeof (long) - size);
+      else
+	collect_register (regcache, regno, buf);
+    }
   else
-    collect_register (regcache, regno, buf);
+    perror_with_name ("Unexpected byte order");
 }
 
 static void
 ppc_supply_ptrace_register (struct regcache *regcache,
 			    int regno, const char *buf)
 {
-  int size = register_size (regno);
-  if (size < sizeof (long))
-    supply_register (regcache, regno, buf + sizeof (long) - size);
+  if (__BYTE_ORDER == __LITTLE_ENDIAN)
+    {
+      /* Little-endian values always sit at the left end of the buffer.  */
+      supply_register (regcache, regno, buf);
+    }
+  else if (__BYTE_ORDER == __BIG_ENDIAN)
+    {
+      /* Big-endian values sit at the right end of the buffer.  In case of
+         registers whose sizes are smaller than sizeof (long), we must use a
+         padding to access them correctly.  */
+      int size = register_size (regno);
+
+      if (size < sizeof (long))
+	supply_register (regcache, regno, buf + sizeof (long) - size);
+      else
+	supply_register (regcache, regno, buf);
+    }
   else
-    supply_register (regcache, regno, buf);
+    perror_with_name ("Unexpected byte order");
 }